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In this work, the kinetics of barium sulfate recrystallization has been studied in acidic 0.01 mol dm sodium sulfate solution using Ra and Ba tracers at very low total radium concentration, i.e. less than 10 mol dm. It was found that the system follows the homogeneous recrystallization model and that recrystallization rates, inferred by the decrease of Ra and Ba in the aqueous solution, are fast. Therefore, even at very low concentrations, below the solubility limit, radium will be retained by barium sulfate-a mineral present in the deep underground repository. [ABSTRACT FROM AUTHOR]

Solid octaaqua(κ2-perchIorato)thonum(lV) perchlorate hydrate, [Th(H20)8(ClO4)](ClO4)3-H2O, 1, and aquaoxonium hexaaqualris(κO-trifluoromethanesultonato)thorium(lV) trisaquahexakis(κO'trifluoromethanesultonato)thorinate(IV), H5O2[Th(H2O)6(OSO2CF3)3][Th(H2O)3(OSO2CF3)6], 2, were crystallized from concentrated perchloric and tritluoromethanesulfonic acid solutions, respectively. 1 adopts a severely distorted tricapped trigonal prismatic configuration with an additional oxygen from the perchlorate ion at a longer distance. 2 consists of individual hexaaquatris(κO-tritluoromethanesulfonato)thorium(IV) and trisaquahexakis(κO-trifluoromethanesulfonato)thorinate(lV) ions and an aquaoxonium ion bridging these two ions through hydrogen bonding. The hydrated thorium(IV) ion is nine-coordinated in aqueous solution as determined by extended X-ray absorption tine structure (EXAFS) and large angle X-ray scattering (LAXS). The LAXS studies also showed a second hydration sphere of about 18 water molecules, and traces of a 3rd hydration sphere. Structural studies in aqueous solution of the hydrolysis products of thorium(lV) have identified three different types of hydrolysis species: aμ2O-hydroxo dimer, [Th2(OH)2(H2O)12]6+, a μ2O-hydroxo tetramer, [Th4(OH)8(H2O)16]8+ , and a μ3 O-oxo hexamer, [Th6O8(H2O)n]8+'. Detailed structures of these three hydrolysis species are given. A compilation of reported solid state structures of actinoid(lV) compounds with oxygen donor ligands show a strong correlation between the An-C bond distance and the coordination number. The earlier reported U–C bond distance in the hydrated uranium(lV) ion in aqueous soistion, confirmed in this study, is related to nine-coordination. The hydrated tn- and tetravalent actinoid ions in aqueous solution all seem to be nine- coordinated. The trivalent ions show a significant difference in bond distance to prismatic and capping water molecules in assumed tricapped trigonal prismatic configuration, while the tetravalent ions seem to form more regular structures, probably because of higher polarization. [ABSTRACT FROM AUTHOR]

The structures of the polynuclear hydrolysis complexes of chromium(lll) formed in acidic and alkaline aqueous solution have been determined by means of extended X-ray absorption fine structure and large angle X-ray scattering. Chromium(Ill) is present as mononuclear hydrated ions below pH 3—4, with the upper limit depending on concentration, ionic strength, and temperature. Chromium(lll) hydrolyzes in aqueous solution above this pH in concentrated aged solutions to mainly cationic tetrameric complexes containing both single and double hydroxo bridges between the chromium(llI) ions. Above pH 5, the solubility of chromium(llI) decreases sharply to form solid hydrated chromium(lll) hydroxide. The solubility of chromium(lll) increases sharply at elevated pH, and fairly concentrated solutions can be prepared in concentrated aqueous solutions of sodium hydroxide. According to the literature, mononuclear tetrahydroxochromate(lll) complexes, Cr(OH)4-, are formed in alkaline aqueous solution. However, this study shows polymeric chains of six-coordinated chromiurn(lll) ions connected through double hydroxo bridges and with two terminal hydroxo groups giving an overall composition of (Cr(OH)4)nn-. This polymer is stable for a long time in solution at pH=15. However, at pH < 15, this polymer precipitates slowly with time, over months, to an amorphous phase with a structure around chromium similar to that in α-chromium(lll) oxide hydroxide. [ABSTRACT FROM AUTHOR]

Two electrodes for anodic water oxidation made by direct synthesis of inorganic catalysts onto conductive carbon fibre sheets are evaluated. As catalysts two Co- and Sb-containing phases were tested, that is, Co3Sb4O6F6 and the new compound CoSbO4. The compounds express large differences in their morphology: CoSbO4 grows as thin needles whereas Co3Sb4O6F6 grows as larger facetted crystals. Despite the smaller surface area the latter compound shows a better catalytic performance. When the compound Co3Sb4O6F6 was used it gave a low increase of +0.028 mV h−1 at an overpotential of η=472 mV after 10 h and a stability of +0.48 mV h−1 at an overpotential of η=488 mV after 60 h. The leakages of Co and Sb were negligible and only <0.001 at % Co and approximately 0.02 at % Sb were detected in the electrolyte. [ABSTRACT FROM AUTHOR]

We explored the use of selected layered double hydroxides (LDHs) of different compositions and obtained by means of different routes (i.e., coprecipitation, anionic exchange and reconstruction) as iodine/iodate adsorbents. The influence of speciation (iodide vs. iodate) on iodine uptake was rather strong, resulting in much lower iodide incorporation. The Fourier transform of iodine K X-ray absorption edge data (EXAFS) of all iodate-LDHs showed a single I-O scattering path of 1.8 Å. Thermal stability and leaching experiments showed that the incorporated iodate and iodide were rather loosely bound in the interlayer space and were easily released under heating to 180 °C and leaching with Milli-Q water and brine solution. [ABSTRACT FROM AUTHOR]

The two dimethyl sulfoxide solvated rhodium(iii) compounds, [Rh(dmso-κO)5(dmso-κS)](CF3SO3)3(1& 1*at 298 K and 100 K, respectively) and [Rh(dmso-κO)3(dmso-κS)2Cl](CF3SO3)2(2), crystallize with orthorhombic unit cells in the space group Pna21(No. 33), Z= 4. In the [Rh(dmso)6]3+complex with slightly distorted octahedral coordination geometry, the Rh–O bond distance is significantly longer with O transto S, 2.143(6) Å (1) and 2.100(6) Å (1*), than the mean Rh–O bond distance with O transto O, 2.019 Å (1) and 2.043 Å (1*). In the [RhCl(dmso)5]3+complex, the mean Rh–O bond distance with O transto S, 2.083 Å, is slightly longer than that for O transto Cl, 2.067(4) Å, which is consistent with the transinfluence DMSO-κS> Cl > DMSO-κOof the opposite ligands. Raman and IR absorption spectra were recorded and analyzed and a complete assignment of the vibrational bands was achieved with support by force field calculations. An increase in the Rh–O stretching vibrational frequency corresponded to a decreasing trans-influence from the opposite ligand. The Rh–O force constants obtained were correlated with the Rh–O bond lengths, also including previously obtained values for other M(dmso)63+complexes with trivalent metal ions. An almost linear correlation was obtained for the MO stretching force constants vs.the reciprocal square of the MO bond lengths. The results show that the metal ion-oxygen bonding of dimethyl sulfoxide ligands is electrostatically dominated in those complexes and that the stretching force constants provide a useful measure of the relative trans-influence of the opposite ligands in hexa-coordinated Rh(iii)-complexes. [ABSTRACT FROM AUTHOR]

Water Splitting Catalytic water splitting is a very active research field, and many organic and inorganic catalysts have been tested for the oxidation reaction that is more challenging to catalyse at a low overpotential than the reduction reaction. Metalorganic catalysts most often survive only for short time period, so inorganic compounds are in general more promising. Several promizing oxide compounds containing cobalt have previously been identified and studied. To investigate direct synthesis of catalytically active compounds and their long time behavior, H. Svengren et al. have synthesized crystals of Co3Sb4O6F6 and the new compound CoSbO4 directly onto carbon electrodes. In their Full Paper on page 568 ff., they show the importance of making long‐term stability tests when ranking the performance of different catalysts. [ABSTRACT FROM AUTHOR]